1. Field of Invention
The present invention relates to an apparatus of a liquid crystal display. More particularly, the present invention relates to a polarizer of a multi-domain vertical alignment liquid crystal display.
2. Description of Related Art
Liquid crystal display (LCD) has many advantages over other conventional types of displays including high display quality, small volume, light weight, low driving voltage and low power consumption. Hence, LCDs are widely used in small portable televisions, mobile telephones, video recording units, notebook computers, desktop monitors, projector televisions and so on, and have gradually replaced the conventional cathode ray tube (CRT) as a mainstream display unit. Therefore, the market is mainly occupied by LCDs due to the high display quality and the low power consumption of the LCDs.
Large size, high resolution, wide view and rapid response time are the main demands on the LCDs. Multi-domain vertical alignment (MVA) is one popular wide view technique in which the vertical alignment technique, where the vertical alignment liquid crystal has a negative anisotropic dielectric constant, and the domain division technique are implemented. In an MVA-LCD, a plurality of protrusions are formed on the thin film transistor (TFT) and color filter (CF) substrates thereof for forming different domains, and liquid crystal molecules in different domains are aligned in different directions, thus achieving the wide view.
FIG. 1A illustrates a schematic view of a conventional multi-domain vertical alignment liquid crystal panel. As illustrated in FIG. 1A, a liquid crystal pixel 102 is divided into four domains by several TFT substrate protrusions 112 and CF substrate protrusions 114. Each domain separately contains liquid crystal molecules 122, 124, 126 and 128 which are aligned in different directions. FIG. 1B is a schematic view of alignment directions of liquid crystal modules in different domains in FIG. 1A. In the four domains, the liquid crystal molecules 122, 124, 126 and 128 are aligned in different directions, thus achieving the wide view.
The MVA technique used in an LCD generally provides at least four alignment domains in one liquid crystal pixel to perform the wide view feature including at least four directions. For the viewing-angle characteristics of the four-domains alignment division, the viewing-angle characteristic of the 45 and 135 viewing directions is poor. A simple compensation method is to use an optical compensating film, such as a biaxial film, to obtain better viewing-angle characteristics.
However, in addition to the viewing-angle characteristic of the 45 and 135 viewing directions, the MVA technique still has insufficient brightness. As described above, the protrusions are formed on the substrates to divide the domains and align the liquid crystal molecules in the MVA technique. These protrusions unavoidably decrease the aperture ratio of the liquid crystal panel, and the aperture ratio directly relates to the brightness of the LCD. When the aperture ratio is increased, the brightness of the LCD is also increased. Therefore, the protrusions used in the MVA technique generally reduce the brightness of the LCD, thus causing the insufficient brightness problem.
Moreover, in the vertical alignment technique, in an OFF state, the liquid crystal molecules are vertically aligned where the alignment thereof is perpendicular to the substrate to represent a dark state. On the other hand, in an ON state, the liquid crystal molecules are tilted to be horizontally aligned by the electric field, where the alignment thereof is parallel to the substrates but not parallel to any absorption axis of the upper or the lower linear polarizing film in the LCD to represent a light state. When two adjacent liquid crystal molecules are tilted by the electric field, the two adjacent liquid crystal molecules typically touch each other because they are too close. And, under the continuous effect of the electric filed, the two adjacent liquid crystal molecules are forced to tilt in directions parallel to the absorption axis of the upper or the lower linear polarizing film. Finally, the alignment of the two adjacent liquid crystal molecules contrarily is parallel to the absorption axis of the upper or the lower linear polarizing film.
Therefore, when this type of liquid crystal pixel is in the ON state, the central position thereof appears to have a dark, cross-like texture because the alignment directions of the liquid crystal molecules at domain boundaries are parallel to the absorption axis as described above. The dark, cross-like texture reduces the brightness of the ON state liquid crystal pixel. Moreover, because the contrast of the liquid crystal pixel is defined as a ratio of the ON state brightness thereof to the OFF state brightness thereof, the dark, cross-like texture also lowers the contrast of the liquid crystal pixel, thus causing insufficient brightness and contrast of the LCD.
Conventional MVA-LCDs have the foregoing insufficient brightness and contrast problems; thus, to maintain high brightness and high contrast of the MVA-LCDs, more lamp tubes are used in the backlight source thereof when the LCDs are designed and manufactured. However, if the number of the lamp tubes in the backlight source is increased, the power needed is accordingly raised, and the heat generated thereby is also much greater. High power consumption decreases the use time of portable electronic devices that widely use LCDs, such as notebooks or personal digital assistants (PDAs), and is harmful during use. In addition, unnecessary heat usually burdens the heat dissipation systems of the LCDs, and also accelerates the loss and reduces the lifetime of the lamp tubes of the backlight source.